1. Field of the Invention
The present invention relates to field emission devices, and more particularly to triode field emission devices and methods for making the same.
2. Description of the Related Art
Field emission is a phenomenon which occurs when an electric field proximate the surface of an emission material narrows the width of a potential barrier existing at the surface of the emission material. This allows a quantum tunneling effect to occur, whereby electrons cross through the potential barrier and are emitted from the emission material.
Field emission devices are used in a variety of applications, such as flat panel displays. A typical field emission device has a diode type structure made up of a cathode and an anode, or a triode type structure in which a grid is interposed between the cathode and the anode, such that the amount of electrons emitted from the cathode is controlled.
In a typical triode field emission device, an insulation layer is provided to support the grid and insulating the grid from the cathode. The insulation layer includes a plurality of uniform micro-holes which expose the cathode. Electrons emitted from electron emitters on the cathode can thus pass through the insulation layer. The micro-holes are difficult to make. Various methods for forming the insulation layer are usually complex, have relatively low precision, and/or are costly. For example, a printing process is a typical method for forming an insulation layer with micro-holes. The printing process has rather low precision.
U.S. Pat. No. 6,692,791 issued on Feb. 17, 2004 discloses a method for manufacturing a carbon nanotube field emission display. The method includes the steps of: providing a substrate; screen printing a first conducting layer on the substrate; sintering the first conducting layer; screen printing an isolation layer on the first conducting layer and a second conducting layer on the isolation layer; etching the second conducting layer and the isolation layer, whereby a cavity exposing the first conducting layer is formed; sintering the second conducting layer and the isolation layer; and forming a carbon nanotube layer on the first conducting layer in the cavity. In this carbon nanotube field emission display, the insulation layer is formed by a method includes the steps of screen printing an insulation layer, and etching a plurality of cavities through the insulation layer to expose the cathode. However, the screen printing process has relatively low precision. In addition, the two steps of screen printing and etching make the process relatively complex and costly.
What is needed, therefore, is a relatively simple method for making a quality field emission device.